TH and Parkinson disease: In characterization of dLRRK knockout Drosophila model on PD related pathogenesis, one study reported knockout of dLRRK exhibited a decrease in tyrosine hydroxylase (TH) immunostaining, shrunken DA neurons, and locomotor activity deficits (26), while three studies reported that the homozygous mutant flies developed unchanged number and pattern of DA neurons as well as a normal life span (27–29).